Smell dysfunction in patients with COVID-19

Abstract

Coronavirus disease 2019 (COVID-19) is the cause of a global pandemic and the object of numerous studies worldwide. COVID-19 has many clinical manifestations, but smell dysfunction has become its unique "visiting card". The purpose of this review is to analyze scientific data on anosmia in COVID-19 based on the results of primary research using PubMed, Google Scholar, and eLIBRARY databases. Olfactory dysfunction is a very common symptom in COVID-19: up to 85% of patients report these subjective sensations, but objective olfactory testing shows a higher prevalence - up to 98%. Up to 27% of patients may experience a sudden onset of anosmia as the first symptom. Therefore, anosmia can be crucial in timely identification of individuals infected with SARS-CoV 2. A feature of olfactory disorders in COVID-19 is the preservation of normal transnasal air flow conditions, when edema, hyperemia of the nasal mucosa and rhinorrhea characteristic of other respiratory viral infections are expressed slightly or aren't expressed at all. Many studies show that the olfactory epithelium of the nasal cavity is an area of enhanced binding, replication, and accumulation of SARS-CoV2, which is due to the active expression of two host receptors (APF2 and TMPS2 proteases) by numerous non-neuronal olfactory epithelium cells. It is supposed that supporting cells of the olfactory epithelium are primarily affected, and olfactory receptor neurons and olfactory bulb neurons are affected secondarily. However, the final clinical and pathophysiological significance of olfactory symptoms remains to be determined.